Scientific Forecaster Discussion
fxus63 kdtx 301851
Area forecast discussion
National Weather Service Detroit/Pontiac Michigan
251 PM EDT sun Apr 30 2017
Rapid fire upper level disturbances/mcv's embedded in moist airmass
with next weaker one seen on GOES r ice channel 5 already lifting
north through western Ohio Valley. Blossoming area of showers on the
northeast flank has limited the destabilization over northern
Indiana, but still enough to maintain showers and possible
thunderstorms into Southeast Michigan late today/this evening. With
the failure of warm front to lift into the state during daylight
hours and limited instability it remains highly doubtful we will see
any severe weather in our County Warning Area. Still, 12z NAM/regional Gem do
indicate 1000-850 mb CAPES nearing 1000 j/kg close to Lenawee County
at 00z, while rap is displaced farther east with The Pocket of
instability, which looks better based off the temps in the 80s over
eastern Ohio. Much like the quantitative precipitation forecast bulls-eyes, models running a bit too
hot. None-the-less...one is always weary with such a strong low
level jet (50+ knots at 850 mb), even overnight as the jet
strengthens further, 65+ knots, but surface based inversion is
expected to hold.
Flood Watch will remain in effect for Tri-Cities and adjacent
counties, as we received solid rainfall today pushing totals to
around 1 inch. Will get additional rain (half an inch to maybe 1
inch) late tonight with the cold front, as the large upper level low
over the Central Plains is finally booted off to the northeast from
the upper level energy working through the northern rockies.
Moisture axis will slide east of Southeast Michigan between 12-14z
with good part of the day under influence of mid level dry slot.
However, good low level cold advection and cyclonic flow will
eventually spread scattered to numerous showers back into the area,
right into Tuesday as 850 mb temps of -4 c settle overhead.
Certainly plausible for graupel to fall with that amount of cold
air. Based of forecasted NAM soundings and local probabilistic wind
forecast, wind gusts of 35 to 40 mph look to be common late in the
day Monday, with gusts at above 30 mph continuing right into Tuesday,
as 992 mb low slowly tracks through the northern Great Lakes. Highs
around 50 degrees on Tuesday will likely be the best we can do.
High pressure building in across the Ohio Valley will keep
conditions dry throughout Wednesday as temperatures remain moderate,
with daytime highs capped in the upper-50s. The next chance for rain
showers will enter Thursday morning into Friday as a low pressure
system pushes in from Tennessee into PA. Pop values will continue to remain
sub-30 across the Metro Detroit area for this potential system as
only the GFS and to some extent the ecwmf solution bring the low
north enough, allowing the precipitation shield to clip southern
Michigan. Breezy conditions and a slightly better chances for rain
showers look to take place throughout Friday as moist-laden
conditions wrap around the low pressure system to its northwest.
Lastly, an upper-level disturbance pushing in from southern Ontario
into the Great Lakes throughout Saturday will bring additional
chances for rain showers. High pressure is then expected to build
over Michigan Sunday into Monday, bringing some relief from the
rain. Otherwise, temperature trends will remain fairly consistent
through the middle and end of the week, with daytime highs remaining
in the upper 50s to lower 60s and lows in the 40s through Sunday.
Moderate easterly winds over northern and Central Lake Huron will
begin to ease this evening as the gradient relaxes. A secondary
increase in easterly flow remains possible across Northern Lake
Huron tonight and early Monday. Winds will turn to southerly and
increase on Monday as low pressure lifts west of Lake Michigan.
Gusts as high as 30 knots look to develop by afternoon and continue
through the overnight hours. The combination of higher waves under
the easterly flow through tonight, transitioning to gusty conditions
on Monday will maintain an extended period of Small Craft Advisory
conditions for Saginaw Bay and portions of the nearshore waters.
Winds are expected to shift to the west behind a cold front on
Tuesday, with windy conditions persisting through Tuesday night.
Widespread rainfall is expected through Monday morning, with
periodic heavy rain possible. There will also be a chance for
thunderstorms during this time. This additional rainfall in
combination with rain that has fallen already this weekend will
result in total rainfall amounts up to 2 inches. The highest
amounts will be focused along and north of a line from Flint to
Harbor Beach. Locally higher totals are possible for areas that
experience thunderstorms, as storms will bring brief periods of
torrential rainfall. Rivers and streams will see significant rises
through the middle of the week, and ponding of water may develop in
low-lying areas and roadways. Flooding is possible, particularly
over the Saginaw Valley.
issued at 120 PM EDT sun Apr 30 2017
Deepening low level moisture north of a warm front will maintain
extensive MVFR/IFR conditions in low stratus and periodic/numerous
showers through tonight. Tougher call on coverage of thunderstorms
given limited instability, but will maintain a mention for this
evening across the Detroit corridor given closer proximity to the
warm front and greater instability over Ohio. Window for additional
thunderstorms will exist overnight as a cold front sweeps through.
The warm front will struggle to lift into the Southeast Michigan
airspace, favoring retention of moderate flow with an easterly
component during this time. Gusty Post-frontal southwest winds
will emerge Monday. Gusts 30 to 35 knots will be attainable.
For dtw...low stratus holds under cold easterly flow through the
evening as a warm front struggles to reach the airspace.
Thunderstorm potential still hinging on attaining some level
instability north of this front. Still some potential, particularly
this evening and again overnight. A defined mention will continue
to focus on the evening window.
//Dtw threshold probabilities...
* high for ceiling 5000 ft or less through Monday morning.
* Low for thunderstorms through tonight.
Michigan...Flood Watch through Monday morning for miz047>049-053-054-060-061.
Coastal flood advisory until 10 PM EDT this evening for miz048-054-
Lake Huron...Small Craft Advisory until 10 PM EDT Tuesday for lhz421-422-441.
Small Craft Advisory until 10 PM EDT this evening for lhz442-443.
Lake St Clair...Small Craft Advisory from noon Monday to 4 am EDT Wednesday for
Michigan waters of Lake Erie...Small Craft Advisory from noon Monday to 4 am EDT Wednesday for